Dragana Rogulja is an Assistant Professor in the Department of Neurobiology at Harvard Medical School. Her lab studies circadian rhythms and sleep.

Artificial light is all around us, and it’s changing the world we live in. What is this doing to our biology? In this talk at TEDxYouth@BeaconStreet, Dragana Rogulja answers this question.

Dragana Rogulja – TEDx Talk TRANSCRIPT

In case you didn’t know, 2015 is the International Year of Light. So, I thought I’d tell you just a little bit about the impact of light on our health.

My lab uses fruit flies to study sleep and wake patterns, but what I want to talk today is primarily light and its impact on health.

So, of course, we live on this planet that spins around its axis as it’s orbiting the Sun. As a consequence of that, one of the basic facts of life on Earth is that you’re exposed to light-dark cycles every single day.

Here you see the side of the Earth that’s facing the Sun, is light, and the other one is dark, and actually, I think we have so much light here that the dark side is kind of washed-out.

But if the light was a little bit lower, you could see that there are lights all over the places on Earth, at least where there’s solid ground, just not above water. And that’s maybe a little bit more clear from this picture which is a composite Google image of Earth from above, at night, and I think that this is a really stunning image.

It’s stunningly beautiful, but it’s also stunning to think about the amount of light that we’re enveloping the Earth on. And at the time of day when, for pretty much all of our evolutionary history, the Earth has been dark.

There’s this funny story that I don’t know if it’s true, but I like it, I think it’s a good story, where in 1994, in LA, police started getting reports of people seeing a strange white cloud in the sky, and they didn’t know what this was. They wondered if they should be worried.

It turned out LA had just suffered a major earthquake which resulted in citywide blackouts. So, many people for the first time in many years, or perhaps the first time in their lives, had an unobstructed view of the night sky.

In fact, what they were seeing was not a trail from some alien spaceship, but it was a glimpse of our own home galaxy, the Milky Way. This may sound quite incredible to you until I show you this next picture.

Here’s a picture that this guy, Todd Carlson, from Canada, took of his house, a fairly typical-looking house, a typical-looking sky, at least for those of us living in Boston, or surrounding areas. You can even make out some stars in the sky.

In 2003, there was a blackout that affected large parts of the United States and Canada, and Todd Carlson lost his electricity, and he was smart enough to take a picture of his house at that time, and this is what it looked like.

And again, here you can see this strange, white cloud in the sky which is the Milky Way. The lights that we are producing as humans, due to our ingenuity, are wiping out, basically, our view of these millions of stars in the sky.

So, if we think about that, this is certainly a shame, because there are a few things that are more magnificent than a view of the night sky.

But we should also think about what is this doing to our health if we’re flooding ourselves with this amount of light pollution?

So I want to I tell you that all throughout your bodies, in all of your organs, you have biological clocks that keep you in sync with the light-dark cycles of your environment that result from the Earth’s rotation. And in your heads you have a master clock, a main clock that synchronizes all of these other clocks in your bodies.

The way that this works is that light travels from a source, such as the Sun, or an artificial light source, through your eyes, and that light information is then conveyed to the brain, to the master clock that’s in a part of your brain called the suprachiasmatic nucleus, or the SCN.

So in your eyes you of course have cells that help you see the stars, that help you form visible imagery. But you also have cells that are not a part of the visual-forming pathways, but rather their role is to capture light information and basically convey it to the brain, to tell the brain what time of day it is.

So, how can I convince you that you have this clock?

Well, if I closed you in a dark room where you would have no external source of light, no alarm clocks, no clocks of any kind, you would still retain rhythmic sleep and wake patterns at least for a little while, because your clock was previously trained to light-dark cycles. And one of the main functions of the clock is to regulate behavioral rhythmicity.

This, of course, is not an experiment that many of you would be willing to subject yourselves to, but, fortunately, there’s an experiment that most of us have participated in, which is traveling across time zones.